She didn’t multiply -1/4 by 12 in order to get -1/4x + 3 = -1
which would change her answer, because then you have to subtract 3 from -1 and get -4. Then divide -1/4 & get 16. It changed to positive because of the division & multiplication rule with two negative numbers.
Hope this helps.
You first
-7 subtract -4 equal to -3
The angle at vertex D is acute.
Triangle DEF is a right traingle.
